Pathlength enhancement of optical measurement of physiological blood parameters

Abstract

Systems and methods for measuring a physiological parameter of tissue in a patient are provided herein. In a first example, a method of measuring a physiological parameter of blood in a patient is provided. The method includes emitting at least two optical signals for propagation through tissue of the patient, detecting the optical signals after propagation, identifying propagation pathlengths of the optical signals, and identifying detected intensities of the optical signals. The method also includes processing at least the propagation pathlengths to scale the detected intensities for determination of a value of the physiological parameter.

What is claimed is:  
     
       1. A method of measuring a physiological parameter of blood in a patient, the method comprising:
 emitting at least two optical signals for propagation through tissue of the patient using a tissue interface positioned at an emission location of the tissue, the at least two optical signals carried over a common optical fiber and emitted by the tissue interface at the emission location; 
 detecting the optical signals after propagation at two or more different detection locations of the tissue separate from the emission location, each different detection location corresponding to one of the at least two optical signals; 
 identifying propagation pathlengths of the optical signals based at least on propagation differences among the optical signals between the emission location and the detection locations; 
 detecting presence of a gap between the tissue interface and the tissue based at least on a propagation pathlength of one of the optical signals; 
 identifying detected intensities of the optical signals; and 
 when the presence of the gap is not detected, processing at least the propagation pathlengths to scale the detected intensities in determination of a value of the physiological parameter. 
 
     
     
       2. The method of  claim 1 , wherein emitting the at least two optical signals comprises emitting a first optical signal and a second optical signal at the emission location of the tissue;
 wherein detecting the optical signals after propagation comprises detecting the first optical signal at a first detection location of the tissue and detecting the second optical signal at a second detection location of the tissue different than the first detection location; 
 wherein processing at least the propagation pathlengths to scale the detected intensities comprises processing a first carrier wavelength of the first optical signal and a second carrier wavelength of the second optical signal, distances between the emission location and each of the first detection location and the second detection location, and the propagation pathlengths of the first optical signal and the second optical signal to scale the detected intensities. 
 
     
     
       3. The method of  claim 1 , wherein processing at least the propagation pathlengths to scale the detected intensities comprises scaling a ratio of the intensities of the at least two optical signals with a ratio of the propagation pathlengths of the at least two optical signals. 
     
     
       4. The method of  claim 1 , wherein identifying the propagation pathlengths of the optical signals comprises determining a phase delay and processing the phase delay with a propagation speed through the tissue for at least one of the optical signals. 
     
     
       5. The method of  claim 1 ,
 wherein detecting presence of the gap between the tissue interface and the tissue comprises comparing at least one of the propagation pathlengths to a propagation pathlength range to determine an invalid application of a tissue interface assembly employed to emit the optical signals for propagation through the tissue. 
 
     
     
       6. The method of  claim 1 , wherein the physiological parameter comprises at least one of a total hemoglobin concentration (tHb) parameter, regional oxygen saturation (rSO2) parameter, and arterial oxygen saturation (SpO2) parameter of the blood of the patient.